ui/gtk: skip any extra draw of same guest scanout blob res

ui/gtk: skip any extra draw of same guest scanout blob res

Any extra draw call for the same blob resource representing guest scanout
before the previous drawing is not finished can break synchronous draw
sequence. To prevent this, drawing is now done only once for each draw
submission (when draw_submitted == true).

v2:
 - removed mutex
 - updated commit msg

Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
Signed-off-by: Dongwon Kim <dongwon.kim@intel.com>
Message-Id: <20210924225105.24930-1-dongwon.kim@intel.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>